A kinetic model of coronal heating and acceleration by ion-cyclotron waves: Preliminary results

We present a kinetic model of the heating and acceleration of coronal proto ns by outward-propagating ion-cyclotron waves on open, radial magnetic flux tubes. In contrast to fluid models which typically insist on bi-Maxwellian distributions and which spread the wave energy and momentum over the entir e proton population, this model follows the kinetic evolution of the collis ionless proton distribution function in response to the combination of the resonant wave-particle interaction and external forces. The approximation i s made that pitch-angle scattering by the waves is faster than all other pr ocesses, resulting in proton distributions which are uniform over the reson ant surfaces in velocity space. We further assume, in this preliminary vers ion, that the waves are dispersionless so these resonant surfaces are porti ons of spheres centered on the radial sum of the Alfven speed and the proto n bulk speed. We incorporate the fact that only those protons with radial s peeds less than the bulk speed will be resonant with outward-propagating wa ves, so this rapid interaction acts only on the sunward half of the distrib ution. Despite this limitation, we find that the strong perpendicular heati ng of the resonant particles, coupled with the mirror force, results in sub stantial outward acceleration of the entire distribution. The proton distri bution evolves towards an incomplete shell in velocity space, and appears v astly different from the distributions assumed in fluid models. Evidence of these distinctive distributions should be observable by instruments on Sol ar Probe.